The invention relates to a device for anchoring in a casing in a borehole in the ground. Such a device may for instance for downhole anchoring relative to a casing or lining of a rotary bottomhole assembly (BHA) for drilling and/or reaming a borehole in the ground, or for anchoring a drive for holding and rotating a casing.
After drilling a hole in the ground, for instance for use as an oil or gas well, for collecting geothermal energy, for storage of thermal energy or for installing a subterranean duct under a canal or other structure, usually a casing is ran into the well bore to act as a wall of the well. Casing strings are typically run into the well bore from the surface and hung from the surface or from an intermediate point between the ground surface and the bottom of the hole (in the form of a liner), each next casing string being passed down via a previously installed casing string. For sealing and holding the casing in place, cement may then be introduced in the annular space between the external surface of the casing and the internal surface of the well bore.
As the casing is run into a newly drilled section of the borehole, obstructions, such as ledges which form in the well bore material during drilling, formation washouts, or debris formed by unstable sections of the well bore wall collapsing, are often encountered. To allow the casing to pass such obstructions, a reamer shoe is conventionally mounted on a lower end of the casing string. The reamer shoe removes irregularities or obstructions from the wall of the bore and thereby facilitates the passage of the casing string and aids cementing.
It is also known to provide the lower end of the casing with an assembly including a motor and a drilling bit and an under reamer coupled to the motor, for drilling the hole as the casing is fed into the ground. The drilling bit drills a hole and is followed by the underreamer that enlarges the hole to a size beyond the bit diameter for allowing the casing and, if applicable, the reamer shoe mounted to the lower end of the casing, to follow the drilling bit and the underreamer. It is also possible to use a drillable or expandable drilling bit. During such operations, the casing is usually rotated driven by a top drive at the ground surface.
The underreamer or expandable drilling bit has cutting or crushing arms, which extend to a contour of a diameter larger than the diameter of the casing, the diameter of the borehole obtained thus typically being sufficient to allow the casing, or the reaming shoe at the lower end of the casing, to follow the underreamer or expandable bit. The blades can be retracted to a diameter smaller than the inner diameter of the casing to allow retraction of the reaming or drilling tool through the installed casing (or at least through the portion of the casing string installed following the drilling or reaming tool).
For such operations, tools are anchored relative to the casing or lining, for instance to hold a drilling tool against a torque resulting from rotation of a drill bit and/or a reamer applied to ground formations being drilled and/or reamed. European patent application 1 581 718 discloses an anchoring device for anchoring a well bore tool by latching and clamping an anchor carriage in a recess in an inner wall of a nipple connected into an end of the casing string. In an embodiment, oppositely tapered flanks of the anchor carriage and a mandrel generate the clamping force. However, in such a device axial loads exerted on the latched anchor carriage cause the anchor carriage to expand, which interferes with a required retraction if it is desired to release the anchor carriage from the recess, if the anchoring is to be released and special features are applied to counteract drag as the anchor carriage is moved through the casing.